Magnesium-base extrusion alloy



Dec. 22, 1964 e. s. FOERSTER 3,162,552

MAGNESIUM-BASE EXTRUSIQN ALLOY Filed June 2, 1961 We/yh/ fierce/22 6f Mam United States Patent 3,162,552 lViAQNESlUM-BASE EXTRUSTGN ALLGY George S. Foerster, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed June 2., 1961, Ser. No. 114,503 7 Claims. (Cl. 148-32) This invention relates to magnesium-base alloys containing silicon and at least one of manganese and aluminum. These alloys can be extruded at speeds as high as 100 feet per minute. Furthermore they are prepared using low cost alloying elements, they are weldable without stress relief, and they exhibit moderately high physical properties in the extruded form.

The alloy of the present invention contains, by weight:

Silicon 0.05 to 1.5 percent. At least one of- Manganese 0.1 to 1.5 percent.

or Aluminum 0.2 to 1.5 percent.

and Magnesium Substantially the balance.

Although manganese and silicon exhibit limited mutual solubilities in molten magnesium, it has now been found that alloys containing both manganese and silicon exhibit desirable physical properties in extruded form. Magnesium-silicon alloys containing 0.05 to 1.5 percent of silicon are thus improved by the addition of from 0.1 to 1.5 percent of manganese. Generally, the two constituents must be considered together in preparing an alloy in that if the mutual solubility of the two metals is exceeded, some of each will separate out on settling the alloy. Even if the melt is not settled, the insoluble portions will not be truly alloyed but merely in suspension.

The single figure in the drawing is a bilinear graph indicating, in a general Way, the proportions of manganese and of silicon which may be employed in preparing compositions which are true alloys and miscible at casting temperatures. A melt having one of these compositions does not change on being settled and decanted. The range of proportions is represented graphically by the area A, i.e., the closed figure bounded by the lines shown connecting the points B, C, D, E and F at the corners of the area A. Alloys containing, initially, proportions of manganese and silicon which correspond to the open area above and to the right of the curved line connecting points B and C will be found, on standing, to have lowered manganese and silicon contents whereby the proportions fall toward area A. By failing to settle, or by sing a very high temperature, such as l800 F., and cooling rapidly, a melt havin manganese and silicon proportions outside area A, it is possible to prepare cast compositions which have about the same properties as the alloy falling within area A but a total composition falling outside area A. Alloys which, on being melted and then settled at conventional casting temperatures, consist of magnesium and proportions of manganese and silicon falling with area A, with or without aluminum addition, are to be considered within the scope of the invention.

Generally, as the amount of silicon is increased, the strength properties of the alloy are increased. The presence of manganese greatly improves the malleahility and the corrosion resistance of thealloy and therefore atleast 0.2 percent of manganese is desirably employed. The preferred Mg-Si-Mn alloy contains from about 0.2 to 0.5

percent of manganese and from about 0.7 to 1.5 percent 3,102,552 Patented Dec. 22, 1954 Let It has also now been found that magnesium alloys containing both aluminum and silicon exhibit desirable physical properties in extruded form. Aluminum additions in the order of 0.2 to 1.5 percent by weight impart increased ductility and improved surface appearance to the magnesium-silicon alloys containing from about 0.1 to 1.5 percent by Weight of silicon. Generally, as the amount of silicon is increased, the strength properties of the alloy are increased. Thus higher amounts of silicon are desired. The preferred Mg-Si-Al alloy contains from about 0.5 to 1 percent of aluminum, and from about 0.8 to 1.5 percent of silicon.

The addition of aluminum to Mg-Si-Mn alloy has been found especially desirable as the presence of aluminum improves the surface appearance of extrusion of this desirable alloy and further improves the ductility of the alloy. This quaternary alloy thus contains broadly 0.05 to 1.5 percent of silicon, 0.1 to 1.5 percent of manganese, 0.1 to 1.5 percent of aluminum, and the balance substantially magnesium, the proportions of silicon and manganese being mutually miscible in molten magnesium, i.e., in the molten alloy.

Upon employing larger amounts of aluminum within the stated range for the quaternary alloy, silicon may be employed in Very small amounts and manganese in somewhat larger amounts. Since, silicon, in high proportions, is not as easily alloyed with magnesium as metals such as manganese or aluminum, the low silicon alloy is easier to prepare. The resulting alloy in extruded form exhibits further increased ductility and improved surface appearance without impairment of strength properties. The most preferred form of the alloy thus contains, by Weight, from 0.2 to 0.7 percent of silicon, from 0.5 to 1 percent of manganese, from 0.5 to 1.2 percent of aluminum, and the balance substantially all commercial magnesium.

While the alloys of the invention may be extruded over a wide range of extrusion speeds, while the metal is at a temperature of at least 550 F, they may be extruded to economic advantage at speeds above about 20 feet per minute, and even more advantageously, they can be extruded at speeds in the range of 50 to feet per minute. At the higher extrusion speeds, the present alloy shows no particular decrease in tensile strength properties, contrary to the behavior of most magnesium-base alloys. In fact, the alloy of the invention frequently exhibits higher tensile strength properties upon being extruded at a higher rate of speed in the range of 50 to 100 feet per minute.

The alloy of the invention is readily prepared according to methods well understood in the magnesium metal art. Magnesium is melted under a conventional flux cover and the requisite amount of silicon and'rnanganese and/ or aluminum added to the melt while the melt is at a temperature of about 1600 F.

Ferrosilicon is usually the source of silicon, although other forms of silicon such as silicon metal may be used, if desired. In the event fcrrosilicon is employed, iron,

. which is sparingly soluble in molten magnesium, normally precipitatesinto the bottom sludge layer of the melt. While manganese may be added to the melt at any time, if ferrosilicon is the source of silicon, the requisite amount of manganese is added to the melt as metallic manganese after the iron settles'out. if aluminum is employed, it is likewise added as metallic aluminum.

After the addition of the alloying components, the metal is brought to casting temperature, usually in the range of 1250 to 1450" F, and cast into billet-s suitable for extrusion stock. The. role of the alloying elements is not entirely understood, but itis believed that the silicon addition precipitates in the casting as the relatively finely divided intermetallic' compound, magnesium silicide.

EXAMPLES In accordance with the present invention, several magnesium-silicon alloys were prepared by alloying together the requisite proportions of magnesium, ferrosilicon, and manganese or aluminum metal. The resulting alloys were separated from the precipitated iron'and each cast as 3 inch diameter billets. The cooled solidified billets were scalped, heated to about 700 F., placed in a preheated.

extruded at various different speeds. The data show good I tensile properties can be'rnaintained even at high extrusion speeds.

By way of comparison a magnesium-silicon binary alloyand two Mg-Al-Zn alloys were similarly prepared, extruded and tested. The test results are listed in thetable.

The extruded metal was in the form of a silicon being further limited to amounts mutually soluble in'molten magnesium at casting temperatures.

3. The method of providing an improved extruded article of magnesium-base alloy which comprises: providing an alloy consisting essentially of, by Weight, from 0.05 to 1.5 percent'of silicon, atleast one of the ductility imparting metals from the group consisting of manganese and aluminum, the amount of aluminum in the presence of at 1 least 0.1 percent of manganese being not more than 1.5 percent and in the absence of manganese being from 0.2 to 1.5 percent, and the amount of manganese in the presence of at least 0.2 percent of aluminum being not more than 1.5 percent and in the absence of aluminum being from 0.1 to 1.5 percent, and the amount of both mangae nese and silicon not exceeding that which is mutually solu-' ole in molten magnesium at casting temperatures, and the balance being substantially magnesium; and extruding the alloy at a ratein the range of 50 to. 100 feet per minute While the alloy. is at an elevated temperature above 550 F.

4. The method of providing an improved extruded article of magnesium-base alloy which comprises: providing an alloy consisting essentially of, by weight, from 0.1 to 1.5 percent of silicon, from 0.1 to 1.5 percent of -manganese, and the balance being substantially magnesium, the proportions of manganese and of silicon being further limited to amounts mutually soluble inmolten magnesium at casting temperatures; and extruding the Table Compositions 1 Weight Physical Strength percent Extrusion Percent Properties in Test No. Speed, Elonga- Surface 1,000s of p.s'.i.

l t/Min. tion Appearance a Si Mn Al Zn TYS CYS TS 1. 4 5 4 27 22 39 0.9 5 3 27 2e 1.4 4 27 17 42 0.9 .50 6 27 19 44 1. 4 75 4 28 17 42 0.9 75 5 27 18 43 1. 3 100 8 26 17 37 O. 3 100 10 Excellent, very 28 17 39 smooth. Comparison 1---- 1.4 50 5 Fair 24 17 38' Comparison 2. 0. 4 3. 0 1. 0 50 15 Excellent 29 1 38 Comparison 3 0.3 1. 3 0.6 100 11 .-.....do 23 11 34 TYS=Tensile yield strength.

CYS Compression yield strength. TS =Ultimate tensile strength.

1 Balance magnesium.

Other magnesium-silicomaluminum alloys containing 0.1"to 1.5 percent oi silcon and 0.2 to 1.5 percent of v aluminum on being prepared and extruded in the manner described in the foregoing examples, exhibit similar high strength properties in addition to a smooth, attractive'surface appearance. r p

Among theadvantages of-the alloys of the. invention are the. improved corrosion resistance, malleability and ductility that it exhibits compared to that of magnesiumsilicon binary alloys, and the combination of strength properties and weldability without stress relief as compared to the magnes ium-alurninum-zinc alloys.

While the invention has been described with particular reference to specific embodiment's, it is to be understood,

I that it .is not to be limited thereto butis to be construed broadly and restricted solely by the scope of the appended Iclaim Q q 1. The magnesium-base alloy consisting essentially of,

"by weight, from 0.1 to 1.5 percent oi silicon, from 0.1 to 1.5 percent of manganese, and the balance being substantially magnesium, the proportions .of manganese and of silicon being further limited to amounts mutually soluble in molten magnesium at casting temperatures.

2. The 'magnesiurn b'a'se Lalloy' consistihg"essentiallyof,

V by weight, from 0.7 to 1.5 percent of silicon,from 0.2 to 0.5 percent of manganese, and the balanrebeing substanr" I tially magnesium,{theproportions ofmangane'se and 'ot alloy at a rate in the range of 50 to 100 feet per minute 50- while the alloy is at an elevated temperature above 550 F.

1 article of magnesium-base alloy which comprises: provid- 5. The method of providing an improved extruded 6. The magnesium base alloy in extruded form which consists essentially of, by weight, from 0.05 to 1.5 percent 7 of silicon, at least one of theductility imparting metals selected from the group consisting of manganese and aluminum, the amount of aluminum in the presence'of at.

least 0.1 percent of manganese being not more than-1.5

percentand in the absence of manganesebeing from 0.2- to 1.5.percent, and the amount of manganese in: the presence of at least 0.2 percent of aluminum being not more than, 1.5 percent and in the absence of aluminumbeing .fromQlt 1.5percent, and the amount of both manga- 7 extruded alloy beingQweldabIe Wlthiilllilfsil'ehs:lelif 5116: f.

nese 'andsilico'n not exceeding that which is mutually s'olnuble in molten magnesium at casting temperatures; and

the balance being substantially"magnesiurn, said alloyhaving been pnshed through an ex tr'usiorr die at a speech inth 1range of 50 tolOO feet perminute "whilefthe alloy, was at Y elevated temperaturej above 5505 1? the 5 having a compression yield strengih of at least 17,900 pounds per square inch.

7. The alloy in extruded form as in claim 6 having the composition consisting essentially of, by weight, from 0.2 to 0.7 percent or" silicon, from 0.5 to 1 percent of manganese, from 0.5 to 1.2 percent of aluminum, and the be ance being substantially magnesium.

References Cite in the file of this patent UNITED STATES PATENTS 1,923,591 Schmidt et a1 Aug. 22, 1933 Grant et a1. Feb' 6, Garm er a1. May 22, Singer Oct. 15, Foerster Dec. 4,

FOREIGN PATENTS Great Britain May 24,

OTHER REFERENCES Metals Handbook, 1948 edition, A.S.M., p. 976. Transactions AIME, September 1951, Journal of Metals, pp. 797-799. 

6. THE MAGNESIUM BASE ALLOY IN EXTRUDED FORM WHICH CONSISTS ESSENTIALLY OF, BY WEIGHT, FROM 0.05 TO 1.5 PERCENT OF SILICON, AT LEAST ONE OF THE DUCTILITY IMPARTING METALS SELECTED FROM THE GROUP CONSISTING OF MANGANESE AND ALUMINUM, THE AMOUNT OF ALUMINUM IN THE PRESENCE OF AT LEAST 0.1 PERCENT OF MANGANESE BEING NOT MORE THAN 1.5 PERCENT AND IN THE ABSENCE OF MAGNANESE BEING FROM 0.2 TO 1.5 PERCENT, AND THE AMOUNT OF MANGANESE IN THE PRESENCE OF AT LEAST 0.2 PERCENT OF ALUMINUM BEING NOT MORE THAN 1.5 PERCENT AND IN THE ABSENCE OF ALUMINUM BEING FROM 0.1 TO 1.5 PERCENT, AND THE AMOUNT OF BOTH MANGA NESE AND SILICON NOT EXCEEDING THAT WHICH IS MUTUALLY SOLUUBLE IN MOLTEN MAGNESIUM AT CASTING TEMPERATURES, AND THE BALANCE BEING SUBSTANTIALLY MAGNESIUM, SAID ALLOY HAVING BEEN PUSHED THROUGH AN EXTRUSION DIE AT A SPEED IN THE RANGE OF 50 TO 100 FEET PER MINUTE WHILE THE ALLOY WAS AT AN ELEVATED TEMPEATURE ABOVE 550*F.; THE EXTRUDED ALLOY BEING WELDABLE WITHOUT STRESS RELIEF AND HAVING A COMPRESSION YIELD STRENGTH OF AT LEAST 17,000 POUNDS PER SQUARE INCH. 